1. Field of the Invention
The present invention relates to a photopolymerizable inkjet ink, an ink cartridge housing the photopolymerizable inkjet ink, and an inkjet printing device containing the ink cartridge.
2. Description of the Related Art
Photopolymerizable inkjet inks using (meth)acrylic acid ester as a base monomer component have been widely known (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-526820). Moreover, it is also known in the art that various functions can be provided to a coating film by adding a polymer component to the photopolymerizable inkjet ink (see, for example, Japanese Patent Publication Application (JP-B) No. 07-010894).
One of the advantages obtained by adding the polymer component to the photopolymerizable inkjet ink is to secure sufficient adhesion of the polymerizable inkjet ink to a relatively smooth base, such as a plastic material, with which it is difficult to penetrate a liquid and secure adhesion of a coating film. When the photopolymerizable inkjet ink contains the polymer component, however, the viscosity of the ink significantly increases due to the contained polymer component. Unless a monomer having sufficiently low viscosity is used as the monomer component in the photopolymerizable inkjet ink, it is difficult to adjust the viscosity of the photopolymerizable inkjet ink containing the polymer component to the range at which the ink can be ejected.
Moreover, many of the monomer components used in conventional photopolymerizable inkjet inks are toxic. Especially, among the (meth)acrylic acid esters, which are inexpensive and readily available, most of the (meth)acrylic acid esters having sufficiently low viscosity have high toxicity in terms of skin sensitization, which causes allergy reactions with skin upon contact with such materials. Accordingly, to attain the photopolymerizable inkjet ink having no problem of skin sensitization and having viscosity low enough to eject the ink at room temperature even when a polymer component is contained is a difficult problem, and this problem has not been yet solved in the conventional art.
Note that, reduction in the viscosity of the photopolymerizable inkjet ink can be easily achieved by adding a diluting solvent, but use of the diluting solvent is not desirable considering the environment, as the diluting solvent is evaporated and released in the atmosphere. Accordingly, use of the diluting solvent in the photopolymerizable inkjet ink should be avoided. Moreover, the viscosity of the photopolymerizable inkjet ink can be also reduced by using a water-soluble monomer as the monomer component, and adding water to the ink. However, such ink cannot expect an effect of penetrating and drying as used on a base, such as the plastic material. Therefore, it is necessary to evaporate the water to dry the ink for accelerating speed of a printing process, for which equipment, such as a heat source, is generally required. Accordingly, use of such ink is not preferable in view of energy saving.